Just when you think a game is going well, Ferguson would say, the roof falls in. It happened to Celtic last night when a mature, deeply impressive performance was disfigured by two goals in the last eight minutes. As group openers go, this was all about the bitter end.
Celtic were coping - more than coping - when suddenly a Cristian Zapata shot struck Emilio Izaguirre and changed the course of the ball and this Champions League match. Instead of going wide it nestled in the corner of Fraser Forster's net. Before they could unscramble their senses they conceded again, when a Mario Balotelli free-kick was saved by Forster only for the rebound to fall into the six-yard box for Sulley Muntari to score again. This was the Champions League baring its teeth and showing its cruelty.
When the hurt lifts, Celtic will reflect that they performed in Italy last night like a team that has never looked more at home. They have had their firecracker moments in the Champions League over the years but the big, scintillating wins have been in the harum-scarum of a throbbing Parkhead. Last night in the mighty San Siro they took on Champions League aristocracy and looked comfortable.
There was a time when Celtic would come to arenas like this intent on an element of damage limitation, thinking first of all of keeping the score respectable. They contributed far more than that here. They looked unperturbed by an AC Milan team which, it had to be said, had none of the flair, menace or power of the great club's vintage sides. Celtic have still to win an opening group game after eight attempts, losing six and drawing two, but this was no ugly, backs-to-the-wall survival mission. They took the game to Milan and might have scripted an entirely different story had Anthony Stokes scored rather than hitting the crossbar with a free-kick just before Milan got their breakthrough.
After a forgivably hesitant opening few minutes, Celtic's first half display became composed and enormously encouraging. On the stroke of half-time the stadium screens showed that the possession had been shared 50-50, a remarkable statistic which confirmed Celtic's organised and comfortable play. They did not really threaten the Milan goal but they had plenty of the ball in the home team's half and moved it intelligently and well. Scott Brown and Kris Commons were especially effective in the middle. Had the deliveries from Adam Matthews and Mikael Lustig not been so poor there might have been even more for Celtic in the middle.
They had a strange chance when German referee Wolfgang Stark punished goalkeeper Christian Abbiati for handling the ball twice, awarding an indirect free-kick which Commons tapped for Charlie Mulgrew to blast into the wall. When Valter Birsa was careless with a passback, Stokes was through. He beat Cristian Zapata but then fired a low shot which the defender deflected into the side-netting.
It was the biggest night of Stokes's Celtic career. When big games have come around in the past he has often been either injured or omitted by Lennon, who has doubted his ability to lead the line against elite opposition. Not this time. However tempting it may have been to include new signing Teemu Pukki, it was Stokes who was handed a starting place.
Celtic had Brown and Mulgrew in front of the back four, then a three of Matthews on the right, Commons inside and Georgios Samaras left. Pukki, Derk Boerrigter, Amido Balde and Nir Biton amounted to £9m-worth of talent on the Celtic bench.
Balotelli cut a frustrated, peripheral figure, spending as much time on his backside as on the ball. Forster saved his early volley and was also a match for a low shot which took a horrible deflection off Efe Ambrose and looked to be spinning inside the far post. Milan's threat was sporadic. Alessandro Matri flashed a header which Forster saved and Antonio Nocerino fizzed a dipping shot just over. Matri scored home-and-away for Juventus when they knocked Celtic out in the last 16 last season, but he faded this time.
In the second half, Muntari stole in at the back post and should have buried a Zapata cross. Samaras then wriggled through three Milan players in midfield and struck a shot which bent away from the far post. It was an open, engrossing match which, frankly, Milan looked resigned to drawing until that deflection. Pukki came on to partner Stokes just before the game twisted away from Celtic.
The Celtic fans were up in the gods in the high third tier of the San Siro. Some of them had discharged a flare when the teams came out - a dumb act guaranteeing yet another Uefa fine for the club - but a performance which shone so brightly eventually fizzled out. Next up, it's Barcelona on October 1. Right now that looks both exciting and a little cruel too.